Controlling factor of polymorphism in crystallization process

The controlling factor and mechanism of the crystallization of polymorphs were investigated in the various systems. The effect of supersaturation was hardly observed in the polymorphic crystallization of both L-glutamic (alpha, beta) and L-histidine (A,B). The temperature effect appeared intensively in the case of L-glutamic acid polymorphs, however, no effect of temperature was observed for L-histidine polymorphs. Such difference of the temperature effect may be related with the difference of the molecular conformation between the polymorphs. In the reactive crystallization of calcium carbonate polymorphs between the calcium chloride and the sodium carbonate solutions, the effect of the concentration (supersaturation) of reactant solutions, the mixing rate of the solutions and temperature on the morphology and the crystallization of polymorphs (calcite, vaterite and aragonite) was observed. The complicated precipitation behavior and the morphological change may be related with the formation of the precursors. The effect of L-phenylalanine on the growth rate and morphology of L-glutamic acid polymorphs was also investigated by the single crystal method. The relationship between the additive concentration and the growth rate of each polymorphs was presented by the equation of the proposed model. The method of the selective crystallization of the polymorphs by controlling the supersaturation degree and the additive concentration was also indicated. (C) 2002 Elsevier Science B.V. All rights reserved.